Arylation of β,γ-unsaturated lactones by a Heck-Matsuda reaction: an unexpected route to aryldiazene butenolides and pyridazinones

Abstract

Recebido em 15/6/10; aceito em 6/8/10; publicado na web em 18/10/10The palladium catalysed coupling of aryldiazonium salts with β-γ-unsaturated lactones under basic conditions has been investigated. Both (3H)-furanone and α-angelicalactone were evaluated as substrates in the Heck Matsuda reaction but both failed to afford the desired arylated butenolides. Under basic conditions, β-γ-unsaturated lactones generate highly nucleophilic enolates that preferentially undergo azo coupling reactions with arenediazonium salts to afford aryldiazene butenolides. The electronic and steric effect of the substituents on the aryldiazonium salt in the azo coupling reaction is described. Aryldiazene-lactone derivatives were obtained in good yields from a highly facile and straightforward procedure. An aminoisomaleimide was formed from (3H)-furanone and cyclised to the corresponding pyridazinones in modest yield.

Evolution and Synthetic Applications of the Heck–Matsuda Reaction: The Return of Arenediazonium Salts to Prominence

“…Compared to the usual Heck reaction, arenediazonium salts have on many occasions demonstrated superior reactivity and selectivity for the same unsaturated systems, although certain nucleophilic olefins like β,γ-unsaturated lactones have been found to be incompatible with arenediazonium salts. [39] In this section, emphasis and discussion will be given to those cases where broad reactant scope is also accompanied by high regio-or stereoselectivity.…”

Photoredox-Catalyzed Synthesis of Alkylaryldiazenes: Formal Deformylative C–N Bond Formation with Alkyl Radicals

“…The recently reported syntheses of indoles, amines, , and aldehydes, , as well as the modular formation of C–C bonds, − use alkylaryldiazenes. Although the synthesis of diazenes by the diazonium salt trapping of alkyl radicals was long reported using reducing metals in excess (Scheme ), − their catalytic use has remained underexplored. − Moreover, these methods generally suffer from tautomerization of the diazene to the corresponding arylhydrazones, as in the Japp–Klingemann reaction, , or employ tertiary alkyl radicals to prevent tautomerization. − Another common disadvantage of these procedures is that they may require additional equivalents of diazonium salts to compensate for the formation of by-products (Scheme ). Given the importance mentioned above of alkylaryldiazenes and the limitations of their preparation from diazonium salts, we reinvestigated their synthesis with the tools provided by the booming field of photoredox catalysis.…”